'Young people just don't have the opportunity to get enough exercise these days and this is beginning to show in the increase in weight-related problems among this age group.' What might be the writer's motive in making this claim?

At the simplest level, 'bias' expresses the difference between fact and opinion. But texts are not always so simple - writers can make a highly-opinionated piece appear factual, or can choose to present facts and statistics in a selective, biased manner. Learning to spot bias will make you a careful, critical reader.